如果类的构造器或者静态工厂中具有多个参数，设计这样的类时，考虑使用Builder模式。尤其是大多数参数都是可选的时候，与使用传统的重叠构造器模式相比，使用

builder模式的客户端代码将更易于阅读和编写，构建器也比JavaBeans更加安全。示例如下

1 public class NutritionFacts { 2     private final int servingSize; 3     private final int servings; 4     private final int calories; 5     private final int fat; 6     private final int sodium; 7     private final int carbohydrate; 8  9     public NutritionFacts(Builder builder) {10         servingSize = builder.servingSize;11         servings = builder.servings;12         calories = builder.calories;13         fat = builder.fat;14         sodium = builder.sodium;15         carbohydrate = builder.carbohydrate;16     }17 18     public static class Builder {19         private final int servingSize;20         private final int servings;21         private int calories = 0;22         private int fat = 0;23         private int carbohydrate = 0;24         private int sodium = 0;25 26         public Builder(int servingSize, int servings) {27             this.servingSize = servingSize;28             this.servings = servings;29         }30 31         public Builder calories(int val) {32             calories = val;33             return this;34         }35 36         public Builder fat(int val) {37             fat = val;38             return this;39         }40 41         public Builder carbohydrate(int val) {42             carbohydrate = val;43             return this;44         }45 46         public Builder sodium(int val) {47             sodium = val;48             return this;49         }50 51         public NutritionFacts build() {52             return new NutritionFacts(this);53         }54     }55 }